Contractualism is a term in philosophy which refers either to a family of political theories in the social contract tradition (when used in this sense, the term is an umbrella term for all social contract theories that include contractarianism),^[1] or to the ethical theory developed in recent years by T. M. Scanlon, especially in his book What We Owe to Each Other (published 1998).^[2]

Social contract theorists from the history of political thought include Hugo Grotius (1625), Thomas Hobbes (1651), Samuel Pufendorf (1673), John Locke (1689), Jean-Jacques Rousseau (1762), and Immanuel Kant (1797); more recently, John Rawls (1971), David Gauthier (1986) and Philip Pettit (1997).